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UM1 - Mintemp error, both hotend and heated bed.

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Was in the middle of a long print today when the machine abruptly stopped with a MINTEMP error.

Restarting the machine keeps the error up in the Ulticontroller, and all temp readings are 0. I would guess that this isn't a faulty wiring issue, for two reasons: 1) I've dealt with wiring-related MINTEMP errors before and this is very persistent - not intermittent/flickery at all, and 2) I have a heated bed, and both the hotend and the heated bed stopped reporting their temperatures simultaneously. (Unless a MINTEMP error caused by the hotend prevents the heated bed temp from being reported... anyone know?)

The machine is a little over a year old, but it's been a serious workhorse and is probably approaching 3000 hours. My guess is that something with the mainboard or arduino has gone south. I have other arduinos I can pop in to to test, but is there anything in particular with the mainboard which might have failed and caused temperature readings to stop working?


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Hmmmm, I have seen some behavior similar to this.

If I turn off the power, like in an attempt to abort a print but don't disconnect the USB then reestablish the 19V power, I get the MINTEMP error. Nothing seems to clear it except removing ALL power including the USB power. Even unplugging the USB with the 19V on won't reset it so it appears locked into this state. I believe that without the 19V power, the 5V power "sags" and puts either the Arduino or the TC amp into a weird state.

I think the MINTEMP error really causes a fit in the firmware. I've seen really weird behavior if the machine is started in the MINTEMP state. Like the controller display filling with blocks (try disconnecting the TC from the amp and turning on the machine).

So given all this, is it possible that you are intermittently losing 19V power? Could the jack be "iffy" becoming temporarily disconnected due to vibration? How about the power brick? Is the line side solidly connected?

If it isn't that, you might get the same behavior if the 12V regulator is going bad.


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I looked up the regulator. One of the few things you can get at RadioShack...


It seems that it has internal thermal protection so is it possible it is overheating? I believe the 12V is only used to feed the Arduino. However, if you modded the UM1, did you hook anything else up to the 12V line? Fans? LEDs?


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If the 12V regulator doesn't work anymore, then the whole Arduino should fail and you shouldn't get anything on your screen.

If your Ulticontroller works (meaning the firmware is running), it means your 12V regulator must be working, too...

You can easily check that if you have a Multimeter. Probe the Arduino's power input jack.

Both (all) temperature sensors are read through one module on the Arduino: The ADC. Maybe the fault lies there?

It could be an ESD damage, where you somehow discharged a high voltage into one of the inputs which damaged the ADC module. There are no ESD protection measures whatsoever - only the fact that the Arduino is quite resistant to ESD. But "resistant" is not the same as "protected", and analog inputs are in fact not very happy if you put a voltage on them.


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Turns out my initial guess was wrong and the problem was indeed a broken wire inside the hotend.

Worth noting though: When a Mintemp error is raised, the machine stops reporting both temperature for the hotend and temperature for the heated bed. This should probably be considered a bug within Marlin, as it makes diagnosis more challenging than it should be.


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